Wind power forum: Introductory talk
Theo von Backströ
Backström
Department of Mechanical and Mechatronic Engineering
University of
Stellenbosch
13 April 2007
Wikipedia
Contents
Wind power: growth and cost
Elementary theory
Resource, intermittency and variability
Siting issues and power plant scale
Conceptual design choices
Feasibility and Economics
Ecology, aesthetics and pollution
Conclusions
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Wind power growth
Wikipedia
Growth
Growing at around 30% per year,
but produces < 1% of word’
word’s electricity
Countries with highest installed capacities:
Germany (21 GW), Spain (12 GW),
USA (12 GW), India (6 GW), Denmark (3 GW)
Countries with highest fractional capacities:
Denmark (18%), Spain (9%),Germany (7%)
2
Cost
2004 cost is 1/5 of 1980s cost
Electricity cost (USA) :
Wind: $56/MWh vs. Fossil: $53/MWh
Electricity cost (UK) :
Wind: ₤30-40/MWh vs. New coal:
₤2525-45/MWh vs. New nuclear: ₤4040-70/MWh
Installation cost: $1600/kw
Elementary wind turbine theory
Wind energy is kinetic energy per unit mass
The turbine slows the flow down
V2
V3
& × KE = ρVAstream ×
P =m
= C p Arotor × ρ
2
2
Hansen
The Betz limit: Cpmax = 16/27 = 0.5926
3
The Betz limit
Flow and pressure drop for maximum power:
It
occurs when the wake velocity is:
1/3 of the wind velocity
The exit KE/unit mass in the wake is then:
1/9 of the upstream value
Velocity through the turbine is the average value:
(1 +1/3)/2 = 2/3 of upstream value
The upstream flow area is then:
2/3 of the turbine disc flow area
Fraction of power extracted is:
2/3×
2/3×(1(1-1/9) = 2/3×
2/3×8/9 =16/27 = 0.5926
The wind resource: USA map
Wikipedia
4
Wind Resource
Cencelli
Map of wind power zones
Power production
Of 3 kW Winglette
wind turbine at
18 m rotor height
Zone Power
(kWh/day)
1.
2.
3.
4.
26.6
16.2
12.0
10.2
Winglette
5
Typical wind time and energy
frequency distributions
The wind blows wherever it pleases. (John 3:8)
Wikipedia
Intermittency and variability
6
Siting issues
Average wind strength:
> 16 km/h (4.5 m/s)
Wind steadiness and availability
Proximity to users
Altitude, temperature Topography
Effect of turbines on each other
Environmental impact
Onshore, nearshore or offshore
Onshore:
Micrositing, e.g. on ridge lines
Aesthetics and tourism
Ecology, e.g. bird and bat life
Nearshore:
Up to 3km from coast
Good wind and high air
density
Wikipedia
7
Offshore:
Wikipedia
Turbines almost invisible from land
Strong, steady winds with high speeds at
low heights
Costs of foundations and grid connection
Maintenance in marine environment
American great lakes
Large scale wind power
Theoretical potential 40
times world’
world’s current
electricity use
By 2010 160 GW
expected to be installed
China: 30 GW by 2020
Germany: 6% → 12%
Denmark: 20% → 50%
Feasibility of > 25% is
not certain
Wikipedia
8
Small scale wind power
Wind mills have
been used for
centuries
Wind pumps and
generators, for
decades
OffOff-grid turbines
require energy
storage
Wikipedia
Conceptual design choices
Type
Flow area – cost,
power intermittency
Turbine height - wind
strength, loading
Flow deflection –
number, width of
rotor blades
Tip speed – noise,
generator type
Wikipedia
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Blade profiles
developed at
the Department
of M&M Engineering
at Stellenbosch by
Nicola Cencelli
Issues:
Stall at prescribed CL
Maximum CL/CD
Maximum CL
Cencelli
Comparative sizes of drive trains
NREL
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Power train layout:
Prof Maarten Kamper
NREL
Feasibility and economics
Wind energy is often directly subsidised
Other energy sources are indirectly subsidised,
e.g. environmental clean up.
Capacity factor is relatively low (≈
(≈30%)
Since almost all costs are capital costs, financing
determines price of electricity
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Ecology and aesthetics
It uses only a small fraction of the air energy
Birds are killed, but very few compared to
buildings, house cats, traffic and pesticides
Conventional farming is possible on wind farms,
due to wide spacing between turbines
Modern turbines are quiet (44 dB) or about the
same as wind noise at 16 km/h
Shadow flicker and aircraft warning lights
Pollution
Electric power is only part of power use
UN’
UN’s IPPC states that pollution mitigation can be
more cheaply achieved by improvements in
building, manufacturing and transport efficiency
Wind turbine manufacture and transport require
energy and fossil fuels
Energy return on investment is a factor 20
No direct long term pollution effects.
Site use is reversible.
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Conclusion
Wind electrical energy has a role worldwide
The Western Cape has a target of 15%
(of 5500 MW) renewable electricity generation
by 2015
Western Cape has a feasible wind resource
We hope to establish a wind energy research
unit at UCT in cooperation with US
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